The present invention relates to vehicle bumper systems having energy absorbers, where the energy absorbers have hollow crush lobes constructed to collapse upon impact at predetermined rates of resistance and energy absorption.
Modern vehicle bumpers often include polymeric energy absorbers positioned on a face of a metal reinforcement beam and that are adapted to absorb impact energy. These energy absorbers often have forwardly-projecting hollow lobes (also called “crush boxes”) that are elongated horizontally and where adjacent lobes are interconnected by straps. The lobes are often hollow “box shaped” structures that, when in a vehicle mounted position, include top and bottom horizontal shear walls, right and left vertical shear walls, and a front wall. However, this concept of spaced-apart elongated box-shaped lobes leads to inconsistent energy absorption across a length of the bumper system and thus varied performance depending on where a pedestrian's leg strikes the energy absorber.
For example, if a pedestrian's leg contacts the energy absorber between lobes during an impact, it will likely encounter two vertical shear walls (i.e. the two shear walls on either side of a particular strap, see the left leg impactor in prior art in FIG. 2), which generates a relatively higher force of impact against the leg. Also, if the leg contacts the energy absorber at a center of a lobe, the leg basically misses any vertical shear wall (see the right leg impactor in prior art in FIG. 2), and hence the rate of energy absorption during impact will be substantially lower. Notably, it is not at all clear what spacing or position or shape of the shear walls (i.e. walls that crush and absorb energy during an impact) on an energy absorber will give a best result, especially given the different densities and materials (i.e. bone, flesh, skin) within a pedestrian's leg and the roundness of a leg.
Notably, the impact against a pedestrian's leg is complex and difficult to replicate, such that various government and insurance companies have developed a standardized pedestrian leg impacting device (also called “standardized leg impactor”) for use when conducting pedestrian impact testing. Specifically, a committee of the United Nations called UNECE has propagated a standard using a pedestrian-leg-simulating impactor 50 (see FIG. 2). The impactor 50 has a center core 51 that is a 70 mm diameter steel rod (which represents “bone”), surrounded by a 25 mm thick foam layer 52 (which represents “flesh”), and that is then wrapped in a 6 mm thick neoprene sleeve 53 (which represents “skin”), producing a total diameter of 132 mm. Since different densities are included through its interior, it is not at all clear what size or shape of lobe, nor spacing of shear walls or lobes, should be optimally provided in energy absorbers for a most uniform “best” resistance profile.
For the above reasons, improvements in energy absorbers with hollow crush lobes are needed to provide both reliable and predictable pedestrian impact characteristics across a length of the energy absorber as well as to provide desired impact characteristics for more severe impacts.